Loudspeaker structure



Feb. 14, 1956 H. F. OLSON EI'AL 2,734,591

LOUDSPEAKER STRUCTURE Filed March 2, 1953 2 Sheets-Sheet l INIENTOR.

Harry 1701/0114 c/a/zn PZEJ'ZLOIZ ATTORNEY Feb. 14, 1956 H. F. OLSONETAL 2,734,591

' LOUDSPEAKER STRUCTURE Filed March 2, 1955 2 Sheets-Sheet 2 H W 5 M a?INVENTORJ m fi'rry F 0/4004 Q Jab]? Prarfazz l ATTORNEY United StatesPatent LOUDSPEAKER STRUCTURE Han-y F. Olson, Princeton, and JohnPreston, Metede conk, N. 1., assignors to Radio Corporation of America,a con poration of Delaware Application March 2, 1953, Serial No. 339,810

3 Claims. (Ci. 181-31) This invention relates to acoustics and moreparticularly to loudspeakers.

There has been developed and marketed a wide frequency range loudspeakerwhich is characterized in that the single speaker has a low frequencycone and a high frequency cone. The low frequency cone is truncated. Thehigh frequency cone is arranged centrally of the larger, low frequencycone, constituting substantially a continuation of the conic surface ofthe larger cone. An example of such a speaker is known, commercially, asthe RCA Duo-Cone. Although the speakers of the type give excellentresults and have found wide acceptance on the market, it has been foundthat the response of the speaker in the range of 2500 to 8000cycles/sec. was somewhat low. Signals in that frequency range aresupplied by the high frequency or smaller cone. The output of a directradiator loudspeaker can be increased by reducing the solid angle intowhich the speaker radiates. However, a symmetrical reduction of thesolid angle, in the case of speakers of the type under consideration,would mean a reduction of the angle of the low frequency cone. Such anexpedient would, obviously, impair the broad directivity pattern of thelow frequency cone.

It is, accordingly, an object of the present invention to provide meansfor improving the output of the high frequency cone of a double-conespeaker without impairing the output of the low frequency cone.

It is another object of the present invention to provide an improveddouble cone, wide frequency range loudspeaker which is characterized inthat the output of the high frequency cone is improved without impairingthe output of the low frequency cone.

It has also been noticed that slight dips occur as certain frequenciesalong the axis of the speaker. These dips, it was determined by thepresent inventors, are caused, at least in part, by sound waves from thesmall, highfrequency speaker being reflected by the surface of thelarger, low frequency speaker.

It is a further object of this invention to provide an improved doublecone loudspeaker in which the foregoing difiiculty is overcome.

A still further object of this invention is to provide an improvedspeaker as set forth in which the reflecting surface of the lowfrequency cone is broken up.

A further irregularity in the output of the speakers was noted withrespect to the low frequency cone. The outer periphery of the large coneis supported by a corrugated annulus which provides a flexibleconnection between the cone and the usual fixed support. This corrugatedannulus resonates at certain frequencies of operation of the large cone.Sometimes this resonant vibration is out of phase with the large coneand sometimes it is in phase with the vibration of the large cone. Suchoperation re sults in irregularities in the response characteristic ofthe speaker.

Yet another object of the present invention is to provide an improvedloudspeaker in which the foregoing difiiculty is overcome.

Still another object of the present invention is to provide an improvedloudspeaker as set forth wherein means are provided which prevent thesuspension annulus from I being substantially a continuation of theconic surface of the larger cone. A number of small cones are secured tothe front face of the conic surface of the large cone.

These small cones are arranged in a non-symmetricalarray with respect tothe axis of the speaker and with their vertices directed toward thefront of the speaker. In addition, a soft foam rubber or sponge annulusis secured in energy absorbing relation to the surface of a corrugatedannulus supporting the periphery of the larger cone.

A better understanding of the present invention may be had from thefollowing detailed description when read in connection with theaccompanying drawing in which:

Figure l is an elevational view of the loudspeaker constructed inaccordance with the present invention,

Figure 2 is an end view partly broken away of one of the diffusing conessecured to the speaker cone,

Figure 3 is a side view of cones shown in Figure 2,

Figure 4 is a crosssectional view taken along the line 4-4 of Figure 1.

Referring now to the drawing in more detail, there is shown aloudspeaker of the type having a high frequency sound radiating cone 2and a low frequency sound radiating cone 4. The low frequency cone 4 issecured at its periphery to compliant member 6 which is in turn sup-,

ported by a rigid cone supporting member 8, commonly referred to as adishpan. The compliant member may be integral with the cone member andconstitute an annulus having a plurality of concentric corrugations 10.The inner end of the low frequency cone is supported by a substantiallysimilar compliant member 12 which is secured to a supporting ring 14carried by the aforesaid dishpan 8. The high frequency cone 2 issupported at its periphery by a compliant member 16 which is carried bya supporting ring 18.

A motor unit for this type loudspeaker is shown and claimed in copendingapplication Ser. No. 51,962, filed September 30, 1948 in the name of thepresent inventors. That motor consists of a permanent magnetic member 20mounted in an outer magnetic shell 22. A pole cap 24 and members 26 and28 define a pair of cylindrical annular air gaps in which the voicecoils 30 and 32, respectively, operate.

It may be seen from an examination of the drawings, particularlyreference to Figure 4, that the high frequency cone 2 is mountedcoaxially with the low frequency cone and constitutes substantially acontinuation of the conic surface of the low frequency cone. Thus thehigh frequency cone defines the solid angle into which the highfrequency cone radiates. In order to reduce that solid angle withoutappreciably altering the radiation characteristic of the low frequencycone a plurality of small conical members 34 are secured to the concavesurface of the low frequency cone. It may be seen that these conicalmembers substantially reduce the solid angle into which a high frequencycone radiates. However, since the low frequency cone operates as apiston the conical members do not appreciably affect the radiationcharacteristics of the low frequency cone.

As has been previously pointed out, when the high frequency cone isoperating, reflections of the sound waves generated thereby arereflected from the surface of the low frequency cone. Since the twocones are mounted coaxially the low frequency cone is symmetrical aboutthe high frequency cone. Therefore, the reflections from the 3 lowfrequency cone will be uniform and will meet at a point on' the axis onthe cones. If the conical members 34 are symmetrically arrayed about theaxis of the cone, the reflections from the low frequency cone may besomewhat diffused butthere will be interference patterns set up.Consequently, to more effectively diffuse the reflections from the lowfrequency cone the conical members are arrayed asymmetrically withrespect to the axis of the cone. The conical members, shown more clearlyin Figures 2 and 3 are made of substantially the same material as theloudspeaker cone. It may be noticed from the drawings that the periphery36 of the conical members is shaped to conform to the concave surface ofthe large low frequency cone. Thus the conical members may be placed onthe surface of the cone and cemented. The slightly added mass due to theconical members does not have a deleterious effect upon the responsecharacteristic of the low frequency cone. Alternatively, the smallerconical members may be protuberances formed in the surface of thespeaker cone while it is being molded.

It was also previously indicated that when the large cone is supportedfrom the periphery by a compliant member such as the corrugated annulus6, the compliant member resonates and produces spurious responsecharacteristics. To overcome such resonant vibrations of the compliantsupport member, an annulus of sponge or foam rubber 38 is employed toabsorb the acoustical energy of the compliant member. The energyabsorbing annulus 38 may be rectangular in cross section as shown inFigure 4 or it may be round or the like. Whatever the cross sectionalconfiguration may be the dimension is such that when the annulus isplaced in one of the corrugations, of the compliant member 6 it does notfit into the bottom of the corrugation but leaves an air space betweenthe bottom of the corrugation and the surface of the annulus. Thus theannulus is mounted in the corrugation in bridging relation thereto. Thepoints of contact between the annulus and'the compliant member arecemented together. Thus arranged the annulus absorbs acoustical energycoupled to the compliant member and accordingly prevents the compliantmember from resonating within the audible range.

Thus it may be seen that there has been provided in accordance with thepresent invention an improved loudspeaker wherein the irregularities andresponse characteristics are substantially improved.

What is claimed is:

l. In a loudspeaker assembly including a sound radiating cone, a rigidsupport means for supporting the periphery of said cone and a compliantcoupling member con-' nected between the periphery of said cone and saidsupport member, said coupling member comprising an annulus having aplurality of concentric corrugations therein, the improvement comprisingan acoustical energy absorbing member secured to said coupling member inbridging relation to one of said corrugations.

2. In a loudspeaker assembly including a sound radiating cone, a rigidsupport means for supporting the periphery of said cone and a compliantcoupling member con: ncctcd between the periphery of said cone and saidsupport means, said coupling member comprising an annulus having aplurality of concentric corrugations therein, the improvement comprisingan acoustical energy absorbing member secured to said coupling member inbridging re lation to one of said corrugations, said absorbing memberbeing an annulus of foam rubber.

3. A loudspeaker comprising a sound radiating cone, a supporting member,a compliant member having a plurality of concentric corrugationsintegral with said cone connected between the periphery of said cone andsaid supporting member, and a rubber annulus mounted in one of saidcorrugations in bridging relation thereto whereby an air space betweenthe bottom of the corrugation and the surface of said annulus isprovided.

References Cited in the file of this patent UNITED STATES PATENTS1,616,553 Rupinski Feb. 8, 1927 1,904,538 Round et al Apr. 18, 19332,549,091 Hopkins Apr. 17, 1951 yan

